Currently, the degree of automatic processing of the financial currency is more and more high, in the process of automatic processing of the currency, it is desirable to obtain and detect the authenticity, new and old etc. information of the currency, so as to reduce the degree of manual intervention and to provide convenience to human on the use of the currency.
In the process of automatic processing, obtaining the thickness of the currency to be processed is a basic detection means. The thickness information can be used to determine the information of new and bad, authenticity, incompleteness or paste of tape etc. of the current currency, the above information is necessary means to determine whether the current currency meets the circulation conditions.
As shown in FIG. 1, a thickness data collecting device used commonly in a current financial self-service equipment includes a conveying roll 1 for conveying banknote, a detecting roll 2 opposite to the conveying roll 1, a plate spring 3 being arranged against the detecting roll 2 on the side opposite to the conveying roll, a distance sensor 4 arranged above the plate spring, with the distance sensor 4 being used for detecting a distance value between the plate spring 3 and the distance sensor 4. In view of the current distance detecting means, in order to obtain the thickness of a piece of banknote 5, a distance d between the sensor 4 and the plate spring 3 when no banknote is conveyed is set firstly, the distance d is referred to as a zero value of the thickness detecting device, and when the banknote passes by, the actual thickness value of the banknote being detected can be obtained by the distance data detected by the sensor 4 actually subtracting the above zero value.
It is well known that the performance of all machinery and electronic equipment will aging along with a period of use time, and the equipment will be subjected to shake due to change of the operating environment or during being moved, thus a change in performance parameter is caused thereof. In terms of the thickness detecting devices, the actual mechanical zero value may fluctuate during detecting the thickness of the banknote. When an inaccurate zero value is used, the detected thickness value is inaccurate too, thus it's unable to meet the use of the financial self-service equipment which requires high precision.
Currently, there are two methods for setting the related zero value, including:                1. fixed zero value method, that is, making the zero value d=d0, where d0 is a zero value constant of a factory setting. This method has the drawback as follow: when the thickness detecting device is used for a long period of time and thus aging, or the equipment is subjected to shock during being moved, the actual zero value will change, however the fixed zero value d0 is still used during actual detection, so that large errors will be caused in the collected thickness data.        2. dynamic zero value method, that is, a zero value is detected each time before a banknote passes by, and which serves as the zero value for detecting this piece of banknote. This method employs real time collected data as the zero value, thus avoiding the affect caused by changes in operating environment and other factors, and being more accurate compared with the fixed zero value. However this method still has the problem as follow: because of the inherent nature of the zero value detecting device itself, there are fluctuations in the collected data, that is, the multiple zero values collected in the same environment are different from each other, when a large deviation arises in the collected zero value, a large deviation arises in the actual thickness detection value, abnormity of the collected thickness data will be caused, thus a instability of the whole self-service financial service equipment is caused.        